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Why Does My AC Click?

While some clicking sounds are normal during system start-up, a continuous click from your AC isn’t. This could mean there is a problem somewhere in your system that requires professional help.

Two major parts of your HVAC unit may cause this click. Depending on where the clicking is coming from, it will need to be fixed, or click here for AC.


Your thermostat has a relay that makes a small clicking noise when it signals your AC to start working. This click is a normal sound and usually only happens once when your system starts to boot up.

If the clicking noise is louder or more frequent than usual, you may have a problem with your thermostat. This is especially likely if your air conditioning system seems to be having problems turning on or starting.

You can test your thermostat by flipping the breaker to turn it off and on again. This will reset the internal circuits and may make the clicking noise go away for a while. However, if the clicking is getting louder or doesn’t stop after you’ve done this, call a professional. Your thermostat may need to be replaced or repaired. Our NATE-certified technicians can check out the problem and help with any repairs needed.


Your outdoor AC unit’s contactor is basically a big switch that turns on your compressor and fan after your thermostat sends it a command to start cooling. You hear a click from the electrical panel whenever the contactor extends to execute that command. If your contactor is faulty, it can’t answer the signal sent by the thermostat and you will hear an ongoing buzzing sound instead of clicking.

Typically, a contactor will click when its electromagnetic coil burns out, usually from too much inrush current or unstable control voltages with low transition times between high peak currents. Dirt and dust ingress into the air gap around the coil can also contribute to contactor failure. The A1 and A2 numbers on the contactor are manufacturer designations for the two terminals that connect electrical power to the magnetic coil.


Capacitors look like small cylinders and work with your air conditioner motors to provide electrical signals that either start them or send a series of jolts to keep them running. They are sensitive to heat and can lose their ability to hold an electrical charge if they get too hot. This can lead to overheating and damage that will require them to be replaced.

The capacitance of a capacitor depends on how close together the two conducting plates are. Conductors that are closer together are able to attract each other more strongly than those that are farther apart, giving them a higher capacitance.

The capacitance of a capacitor is measured in farads or F. The capacitance of a capacitor increases as the voltage on its plates decreases, and vice versa. This gives the device a kind of dynamic memory. It can also filter out power line hum to allow signal circuits to operate smoothly. It can even tune radios to particular frequencies.


If you hear a clicking sound while your air conditioner is running and it’s repetitive, it could mean that the fan blades are hitting something inside the unit. This may be as simple as an obstruction in the blades, but it could also indicate that a part is dying or that wiring issues are present. Either way, you’ll need a professional to diagnose the problem and fix it.

If the clicking starts out slow and gets faster over time, it’s likely that the fan is contacting another component as it spins. This usually means that the fan is touching something inside the compressor, which requires professional attention to avoid damage to the unit.

If the click is loud and continuous, it’s most likely a capacitor issue. This is a serious problem that should be addressed right away before it fails completely and damages the compressor.

Jeffrey Lopez

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December 2023